Abstract: The vertical distribution of organisms in the sediment indicates that animals can be present as deep as 15 cm although at very low abundance at such depths (Fig. 4, Fig. 5 and Fig. 6). Oligochaetes and nematods are the only groups able to deeply penetrate into the sediment at significant densities (Fig. 4) in contrast to all other groups, which stay closer to the sediment surface. Maximal densities however seem to shift to the sediment surface with increasing bathymetric depth, as suggested in Fig. 5 and Fig. 6, so that all animal groups are more concentrated near the surface in the deepest parts of Lake Baikal. In such case, the depth of sediment mixing due to bioturbation appears to decrease with increasing bathymetric depth (Fig. 2b).

Abstract: The vertical distribution of organisms in the sediment indicates that animals can be present as deep as 15 cm although at very low abundance at such depths (Fig. 4, Fig. 5 and Fig. 6). Oligochaetes and nematods are the only groups able to deeply penetrate into the sediment at significant densities (Fig. 4) in contrast to all other groups, which stay closer to the sediment surface. Maximal densities however seem to shift to the sediment surface with increasing bathymetric depth, as suggested in Fig. 5 and Fig. 6, so that all animal groups are more concentrated near the surface in the deepest parts of Lake Baikal. In such case, the depth of sediment mixing due to bioturbation appears to decrease with increasing bathymetric depth (Fig. 2b).

Abstract: The vertical distribution of organisms in the sediment indicates that animals can be present as deep as 15 cm although at very low abundance at such depths (Fig. 4, Fig. 5 and Fig. 6). Oligochaetes and nematods are the only groups able to deeply penetrate into the sediment at significant densities (Fig. 4) in contrast to all other groups, which stay closer to the sediment surface. Maximal densities however seem to shift to the sediment surface with increasing bathymetric depth, as suggested in Fig. 5 and Fig. 6, so that all animal groups are more concentrated near the surface in the deepest parts of Lake Baikal. In such case, the depth of sediment mixing due to bioturbation appears to decrease with increasing bathymetric depth (Fig. 2b).

Abstract: In all abyssal stations, densities are never over an average of c. 3100 individuals m−2 (Fig. 3, Table 1). In contrast, the shallow station (CON01-427, Posolskoe Bank) harbours the highest observed densities (oligochaetes reach densities as high as 13573 individuals m−2 on average). Gammarids are present in this latter station at 128 m deep, while they are absent from all deep stations. The presence of some groups is anecdotal, such as Hydrachnidia (one specimen in a core at 388 m and two specimens in a core at 625 m) and chironomid larvae (two larvae in a core at 625 m). Interestingly, the two deepest Vydrino cores (CON01-105-7, 600 m, and CON01-106-3, 700 m) are virtually free from animals, suggesting that these stations are perhaps the best choice for the study of stratigraphy and climate proxies.

Abstract: Diatom-inferred snow depth reconstructions for BAIK38 using uncorrected taxa (Fig. 5a–c) show similar trends throughout the study period, with all or only five taxa in the model; snow depth levels are marginally higher in zone 2 in comparison to zones 1 and 3. However, error values are large in comparison to the changes observed. The snow depth reconstruction using corrected diatom abundances (Fig. 5d) shows a somewhat different response. Low values characterise the period coincident with the MWP (between c. 880 AD and c. 1180 AD), which increase into the LIA, reaching peak depths between 1500 and 1775 AD. After then, snow depth values decline to their lowest values in this study by c. 1900 AD. In recent decades, snow depth values appear to increase slightly again up to the top of the core dated at 1994.

Abstract: Preservation differences can be used as correction factors to recalculate the relative abundances of each of the five dominant plankton taxa in BAIK38 and are depicted in Fig. 4. The resulting profile shows that Synedra acus is now the dominant taxa in zone 1 of the core, with other taxa being present at abundances generally less than 10%. At the zone 1/2 boundary, S. acus declines and is replaced by Cyclotella minuta and, to a lesser extent, Aulacoseira skvortzowii and Aulacoseira baicalensis. This profile is different from the relative abundance profile in Fig. 3, as S. acus values decline to very low values by c. 1400 AD, and C. minuta increases to peak values between c. 1525 and 1650 AD. Furthermore, the profile indicates that A. baicalensis remains common throughout this zone. Towards the zone 2/3 boundary, taxa more characteristic of warmer waters increase earlier than previously suggested at c. 1750 AD.

Abstract: Fig. 3 is the diatom stratigraphy of dominant phytoplankton taxa for BAIK38 expressed as relative percentages, plotted against the age scale. Zone 1 (c. 880 AD–c. 1180 AD) is dominated throughout by the autumnal blooming species Cyclotella minuta, while Aulacoseira baicalensis and Synedra acus (both of which bloom in spring) are also present in lower but similar proportions (c. 15%). Zone 2 (c. 1180 AD–1840 AD) is characterised by an increase in C. minuta values in excess of 80% relative abundance, which are sustained virtually throughout the zone. During this time, other taxa are present at only very low abundances, while some (e.g., Stephanodiscus meyerii and S. acus) are frequently absent. Zone 3 (c. 1840 AD–1994 AD) is characterised firstly by a decline in relative abundance of C. minuta to its lowest levels in the profile, up until c. 1950 AD. This decline is accompanied by concomitant increases in A. baicalensis and, to a lesser extent, Aulacoseira skvortzowii and S. meyerii.

Abstract: Calculations were based on factors established for 89 water samples across Lake Baikal in July 2001 (see text). The traps were deployed for about 16 months and the core top spanned c. 7 years (see text).According to the contribution to the chlorophyll a-model shown in Eq. (1), the chlorophyll a content in the water of the south basin in July 2001 was composed of 30% Bacillariophyceae plus Chrysophyceae, 44% Chlorophyta, and 26% cyanobacterial picoplankton. In the 40-m trap, in contrast, 87% of the chlorophyll a originated from Bacillariophyceae plus Chrysophyceae, 11% from Chlorophyta, and 2% from cyanobacterial picoplankton (Fig. 5). The percentage contribution did not change with the water depth, as the same composition was found in the deepest traps (Fig. 5).

Abstract: Fig. 4 visualises differences in the degradation between the organic compounds, chlorophylls, and carbon. The chlorophyll a/carbon ratio decreased with depth, indicating that organic carbon is more slowly degraded than chlorophyll a (Table 6 and Fig. 4), whereas the pheophytin a/carbon ratio and the pyropheophytin a/carbon ratio increased with the depth, indicating the formation of pheophytin and pyropheophytin with depth (Table 6 and Fig. 4). Best fits for the chlorophyllide a/carbon ratio and pheophorbide a/carbon ratio vs. depth were also linear regression models, but they were not significant (Fig. 4).

Abstract: During 16 months of deployment, 239 g m−2 dry matter settled in the 40-m trap, with an average flux of 14.9 g m−2 month−1 (Table 2 and Fig. 2). The content of organic carbon was 21.9% at that depth and that of total nitrogen 1.6% (Table 2 and Fig. 2). The resulting atomic C/N ratio of 15 indicated that the sedimented material resulted from the autochthonous production by suspended phytoplankton and that terrigenous input is likely to be negligible at that site. The amount of pigments gathered during the 16 months deployment in the 40-m trap was 193.1 μmol m−2 for chlorophyll a and 797 μmol m−2 for chlorophyllide a+pheopigment a. The average flux was hence 61.8 μmol m−2 month−1 settled chlorophyll a+chlorophyllide a+pheopigment a (Table 1). It is worth noting that the replicate samples of the 40-m trap deviated strongly (coefficient of variation: 60.5%), whereas the coefficients of variation for the replicate samples in the traps